Lignite char barbecue briquettes and method of making them



Nov. 6, 1962 s. v. MARGoLlN ETAL LIGNITE: CHAR BARBECUE BRIQUETTES AND METHop 0F MAKING THEM Filed sept. 9; 1960 United States Patent Office 3,062,629 Patented Nov. 6, 1962 3,062,629 LIGNITE CHAR BARBECUE BRQUETTES AND METHOD F MAKING THEM Stanley V. Margolin, Auburndale, Russell J. Bowen, Medford, John F. Angeline, Topsfield, and Frederick W. Laiert, Jr., Winchester, Mass., assgnors to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Filed Sept. 9, 1960, Ser. No. 54,909 Claims. (Cl. 44-15) This invention relates lto the manufacture of briquettes by a process which includes the steps of low temperature carbonization of solid carbonaceous fuels, more particularly lignite coal, to produce a char which is free of objectionable odors but which retains a substantial amount of its original volatile matter, and the production from this char of briquettes having desirable chemical and physical properties which make them particularly useful as barbecue briquettes.

Barbecue briquettes are now commonly made from hard wood charcoal. Although this charcoal makes an excellent barbecue briquette, it is relatively expensive. Hence it is desirable to provide a barbecue briquette having the principal advantages of a charcoal briquette, particularly low odor content and rapid ignition, but at a much lower cost.

Char for use in making commercial or fuel briquettes is ordinarily made from lignite or similar low-grade coals by carbonization to remove the tar and certain other materials. This carbonization has not required a close degree of control inasmuch as there has been no particular requirement for attempting to retain non-tar combustible volatile matter. In fact, such carbonization generally takes place at temperatures well in excess of 600 C., e.g., around 700 C., at which point all tar components are removed together with all, or substantially all, non-tar volatile matter. Efforts to make these briquettes more readily ignitable have led to adding promoters such as sodium or calcium nitrate. These, however, present combustion hazards; there have been many instances of spontaneous combustion of such briquettes held in bulk storage.

Volatile combustion matter, as referred to herein, means all non-tar combustible matter which volatizes during the complete carbonization of solid carbonaceous fuels, e.g. at temperatures around 700 C., as indicated above.

In contrast, the production of char suitable for making barbecue briquettes requires the removal of the tar, so as to reduce the odor of the product, especially when burning, while at the saine time retaining as high a content of volatile combustible matter, at least 10%, as is possible. This high content of volatile matter is essential in order to facilitate ignition of the nal briquette. Since the removal of tar components proceeds simultaneously with the removal of volatile combustible matter, with increasing temperature, a very careful control of carbonization conditions is required in order to maintain the desired high content of volatile combustible matter while still removing the entire tar content, or at least the major part of the tar to the point where the char is essentially tar-free.

In accordance with the process of the present invention, the carbonizing of lignite or other solid carbonaceous I fuel is carried out in an internally heated retort, through which such solid fuel moves continuously from top to bottom through three zones. The raw lignite or other solid carbonaceous fuel first passes into a drying zone where it is heated and dried to reduce the water content from its initial content of about 3542% to about 7-9%. The solids continue downward through the retort into a carbonizing zone, where they are subjected to treatment by hot combustion gases and wherein the zone temperature is closely controlled by the addition of cooling gases. The resulting char finally moves into a cooling zone, after having been stripped of its tar content in the carbonizing zone, and is thus cooled by recycling cooled off-gas from the carbonizer, which olf-gas has been stripped of its tar content. The cooled off-gas may be replaced in whole or in part by any cool inert gas for this purpose of cooling the char. The hot combustion gases are introduced in a substantially uniform pattern around the periphery of the carbonizing zone, The recycled cooled olf-gas contains volatile combustible matter, in various proportions depending largely upon the constitution of the original solid carbonaceous fuel. It is usually preferred to recover the heating value of this volatile combustible matter by burning it for example with a conventional hydrocarbon fuel and air, to provide the aforesaid hot combustion gases and/or the heat for the drying zone.

The treatment in the carbonizing zone is controlled by adding small amounts of cooling gas to the zone at substantially the same points as those where the heating gases are introduced, in such a manner that the temperature in the carbonizing zone has an average variation of not -more than about 10 C. and preferably no more than about 5 C. from the prescribed optimum operating temperature. By regulation of the rates of ow to each of the aforesaid points in the carbonizing zone, the desired temperature control is achieved. Local variations in the volatile matter content of the char in the carbonizing zone can be corrected by control of this cooling gas addition to the area concerned, thereby controlling the ternpera-ture in that area.

It is a feature of this invention that either the cooled, cleaned, recycled olf-gases from the carbonizing zone, or cool inert gases are introduced into appropriate areas of the retort for cooling and temperature control purposes. As already indicated, the recycled gases are stripped of -tars and other odorants so as to avoid re-introducing these odorants into the charge. Inasmuch as the char Will readily adsorb such odorants, they must not be present in the recycled gas, either in the portion used as fuel or in that used for cooling and temperature control.

In order to produce good barbecue briquettes, the char must also be subjected to certain treatment steps after it leaves the retort. These steps include the removal of any residual pyrte thus reducing this source of sulfide odors to a point where they are not detected in the burning of the briquette, the crushing of the char to a suitably small particle size, thereby improving its ignition characteristics, and the binding of this crushed char into briquettes with a small amount of a binder which does not introduce undesirable odors or possible explosive or spontaneous combustion hazards, which is unaffected by extremes of climate such as high temperatures and/or high humidity, and which does not smear over the surfaces 3 of the char particles, but rather binds them together essentially at just their points of contact.

This invention will now be described in more detail in connection with the accompanying drawing, which shows in schematic and flow sheet fashion how it may be performed. Specific reference will be made to the treatment of lignite, although other solid carbonaceous fuels may be treated similarly.

Raw lignite from the mine is first passed through a scalping operation 10 where pyrite lumps are removed. The lignite is then broken in a Crusher 12 to convenient size, say 1A to l inch diameter particles, after which it moves to feed hopper 14 arranged to supply the lignite feed to the retort 16.

Retort 16 comprises three zones, a drying zone 18, a carbonizing zone 20, and a cooling zone 22. Drying zone 18 is provided with several ports 24 spaced evenly around the lower part of its periphery, through which ports hot combustion gases pass from burners, one of which is shown at 26. One or more vents 2S are provided for conveying away exhaust gas and vapor. The temperature in zone -18 is maintained high enough to reduce the water content, as already stated, from say 35-42% to 7-9%, without removing any substantial amount of tar, preferably about 12S-150 C.

Between drying zone 18 and carbonizing zone 20 is a restricted area 30, which keeps essentially separate the operations in the two zones, while permitting ready flow of lignite lumps and particles from zone 18 to zone 20. Due to the restricted area 30, the off-gas from zone 20 may be removed from the latter without passing to any significant extent into zone 18 and there becoming diluted with the gases and vapors (e.g., water vapor) from the drying zone 18.

Carbonizing zone 20 is provided with several ports 32 spaced evenly around the lower part of its periphery. Through these ports hot combustion gases pass from burners, one of which is shown at 34. This zone is maintained at a temperature adequate to remove substantially all of the tar content, but to retain about 12 to 20% of other volatiles. The temperature range of operation is between 500 and 550 C., with control of temperature between plus-or-minus to 10 C. One or more vents 35 are provided for conveying olf-gas away for further treatment. The lower end of carbonizing zone 20 is defined by a grate 36, located just below ports 32. The lignite lumps and particles pass freely through this grate into cooling zone 22.

Cooling zone 22 is also provided with several vents 38 spaced evenly around its periphery and intermediate the upper and lower limits of the zone. Grate 40 is located below these vents 38, and like grate 36, permits ready passage of lumps and particles of lignite and promotes even distribution of the lignite mass throughout the zone. Zone 22 terminates at its bottom end in discharge openings 42, adjacent to which are ports 44 where cooling gas is admitted. The temperature and quantity of cooling gas introduced are such that the char leaving the retort 16 is at a temperature of about 20D-220 C.

The off-gas from carbonizing zone 20 contains the tars from lignite, and also a considerable amount of volatile combustible matter. As already stated, the tars are undesirable odor-imparting substances and, hence, are not wanted in the final briquette. The volatile combustible matter, however, represents a valuable fuel component, and since its combustion as a fuel constituent for heating retort 16 does not impart undesirable odors to the nal product, it should be recovered. This is done by leading the off-gas from vent or vents 35 to conventional removal equipment 50, wherein the tar is precipitated and removal with the aid of cooling water introduced for the purpose. The off-gas is thus brought down to approximately ambient temperature or slightly above, say 40 C. 'Ihe cooled cleaned off-gas, free of tars, is then circulated through appropriate ducts to various stations in retort 16. Duct 52 controlled by valve S4 carries that portion of the off-gas used for cooling purposes; duct 56 carries the portion which is used as a fuel. Duct 52 is divided into two branches: duct 53, controlled by valve 59, which delivers cooled clean gas into ports 44 in the bottom part of cooling zone 22, and a series of ducts 60, each controlled by a valve 61, which deliver another portion of said gas into each of ports 32 in the carbonizing Zone. Duct 56 is divided into ducts 62 and 64, controlled respectively by valves 63 and 65, and leading to each set of burners 34 and 26 respectively.

Cool inert gases instead of recycled cleaned off-gas may be introduced for cooling through duct 66 controlled by valve 67. The relative proportions of cool inert gas and cooled off-gas are controlled by regulation of valves '54 and 67, whereby the cooling gas in ducts 58 and 60 may range anywhere from 100% of the former gas to 100% of the latter.

The volatile combustible matter of the char, cooled, following the temperatures of operation prescribed, upon emergence from the retort is about 10-l5% by weight of the total weight of solids discharged.

In addition to the supply of off-gas, each of burners 26 and 34 receives a supply of gaseous fuel, e.g., a gaseous hydrocarbon, through valve-controlled lines 68 and 69 respectively. Air for combustion is supplied through valvecontrolled lines 70 and "i2 respectively. Burners 34 also receive off-gas leaving the cooling zone 22 through vents 38. This off-gas is of substantially the same composition as when it entered through ports 44; it has, of course, become heated in its passage through the char in zone 22.

The temperature in the carbonizing zone depends principally upon the amount of heat supplied by burners 34 and the rate of flow and temperature of the lignite entering that zone from zone 18. The line control of the ternperature in zone 20 is, however, accomplished by the introduction of cooling gas from ducts 60 through ports 32. Since each duct 60 is controlled by its valve 61, the quantity of cooling gas introduced into any portion of zone 20 can be controlled as desired. Obviously, the heat supplied to zone 20 or to any portion thereof can be controlled in known manner by the supply of fuel and air to each burner 34.

The char discharged through openings 42 is moved by suitable conveying means to an air table or other means 82 for removing pyrite fines. This step 82 is omitted in the event that the char comes from a solid fuel source which is essentially devoid of pyrite. Thence it passes to comminuting means 84, such as a hammer mill, where it is reduced to particles of 40 mesh size and less. These particles then pass into mixing device 86 where they are mixed with the binding medium, which is made up of starch and water. The resulting product is then pressed into briquettes of the desired size. These are dried and then put up in any desired way for shipment as the final product briquettes.

l Reference has already has been made to the precautions which must be observed in handling the char after it leaves retort 16. Reduction in particle size to 40 mesh and less is essential in order to provide a large surface area, thus facilitating ignition of the briquettes. A particle size of 50-65 mesh, with a volatile combustibles content of about 13%, gives good results.

Starch is the binder which meets the requirements of this invention. Best results are obtained by using a precooked starch of very fine particle size, as starch so treated gives a better binding effect per unit weight of it, and hence less is required for a given strength of product. The starch particles should be liner than 200 mesh, and preferably minus 270 mesh. The starch content of the final briquette does not exceed 10%, and may be as low as 3%. The particle size and quantity of starch bindei used assures that the char particles are not coated witl the binder, but instead are bound together primarily by the presence of starch at points of mutual contact of the char particles. There is thus provided a porous structure, or more accurately a microporous structure since the pores are hardly visible to the naked eye, which is much more easily ignited than it would be if the pores were filled with binder or other substance.

Starch ordinarily contains some protein, which may cause odor problems in the final briquettes when the 4higher limits of starch are used. These odor problems can be reduced or eliminated by using a starch from which more or less of the protein has been removed, and/ or by keeping the amount of starch as low as possible. Another modification is to use the heat of the char for cooking the starch, inasmuch as the char leaves retort 16 at around ZOO-'220 C., and by the time it reaches mixer 86 it can still have a temperature sufiiciently about 100 C. to effect such cooking.

The starch particles and char particles are first mixed together uniformly in mixer 36, in such proportions that the starch makes up 3 to 10% by weight of the mixture. Water is then added and homogeneously mixed. The amount of water in this final mixture is about to 25%. This mixture is pressed at about 5000 to 10,000 p.s.i. in conventional briquette-making equipment 88, and dried to a Water content of 4 to 8% in suitable drying equipment 90. This dried briquette product is then ready to be shipped to market.

The following is a specific example of the manufacture of barbecue briquettes using lignite from the Dickinson, North Dakota, seam. This lignite contains about 41% Water, and on the dry basis it analyzes 43% volatile matter and tars, 46% fixed Carbon, and 11% ash. This is crushed to about 1/2 to 1" size, and fed to the retort, where it is first subjected to a temperature of about 130 C. in the drying zone 18, where it loses 75 to 80% of its water content. It then passes into the carbonizing zone 20 where it is subjected to a temperature of 510 C. i5 and where the tar content and the remaining water are removed, along with light oils, and a portion of the volatile matter. Thence the resulting char moves into cooling zone 22, where it is cooled by cool tar-free off-gases originating in zone '20. Inasmuch as these gases contain volatile combustible tar-free constituents from the carbonizing zone, a portion of them is also used as part of the supply of fuel for heating the combustion zone. The char upon emerging from the retort contains 12-13% of its total weight as volatile combustible matter. The other 87- 88% consists of about 80% carbon and 20% ash, along with not over about 1% pyrite. The resulting char from the retort, after removal of the pyrite fines and crushing to 60 mesh, is mixed with 3 to 4 parts by weight dry precooked starch of 270 mesh, and then with 12 to l5 parts by weight water, to a homogeneous mixture, pressed to form briquettes, and dried to 6% Water content.

Modifications to meet the requirements of lignites of different characteristics as Well as other solid carbonaceous fuels will be evident to those familiar with this art, and are included within the scope of the claims which follow.

We claim:

1. A process for treating lignite which comprises subjecting the lignite to a `drying step to remove the major part of its Water content, subjecting the resulting dried solids to a carbonizing step at 500 to 550 C. to remove in gaseous form the tar content, the balance of the water, and a portion of their non-tar volatile combustible matter, leaving in said char an amount of volatile matter equal to about 10 to 20% by weight of said char, controlling and maintaining the temperature of said carbonizing step within the aforesaid temperature range by introducing cool clean inert gas into the zone of said carbonizing step, removing the tar from and cooling the gas given off from the carbonizing step, recirculating said gas into contact with the `char emerging from said carbonizing step to cool said char, Ireducing the char to fine particle size, of 40 mesh and less, mixing it with a starch-and-water binding medium, the amount of starch being such as to bond the char particles at their points of mutual contact, but not sufficient to coat said particles significantly, the particles of said starch being ner than 200 mesh, pressing the mixture into briquettes, and drying the briquettes.

2. A process according to claim 1 further characterized by the step of removing pyrite particles from the char following the cooling step.

3. A process according to claim l wherein the fuel for supplying heat both to said drying step and to said carbonizing step is composed partly of said cooled off-gas from which tar has been removed and partly of a hydro carbon fuel gas.

4. A process for treating lignite which comprises subjecting the lignite to a drying step to remove the major part of its water content, subjecting the resulting dried solids to a carbonizing step at 500 to 550 C. to remove in gaseous form the tar content, the balance of the Water, and a portion of their non-tar volatile combustible matter content leaving in said char an amount of volatile matter equal to about 10 to 20% by weight of said char, introducing a portion of cool, clean inert gas adjacent the carbonizing step to control the temperature thereof, and another portion of cool, clean inert gas into contact with the char emerging from said carbonizing step to cool said char, reducing the char to fine particle size, of 40 mesh and less, mixing it with a starch-and-water binding medium, the amount of starch being such as to bond the char particles at their points of mutual contact, but not suicient to coat said particles significantly, the particles of said starch being finer than 200 mesh, pressing the mixture into briquettes, and drying the briquettes.

5. A process for treating lignite which comprises drying crushed lignite at 12S-150 C. to remove at least 75% of its water content, subjecting the dried lignite to hot products of combustion in a carbonizing zone at 500-550 C. to drive off in the form of an off-gas the remaining water, the tars, and a portion of the non-tar volatile combustible matter, leaving in said char an amount of said volatile matter equal to about 12 to 20% by weight of said char, removing the tars from said offgas and cooling it to about ambient temperature, circulating a portion of said cooled off-gas to cool the lignite char emerging from the carbonizing step to about 200- 220 C., circulating another portion of said cooled offgas to serve as yat least a part of the fuel supply for forming said hot products of combustion; circulating a third portion of said cooled off-gas into said carbonizing zone to control the temperature thereof within prescribed limits; then separating out any residual pyrite from the resulting cooled lignite char, reducing the lignite char to below 40 mesh, mixing the comminuted char with 4dry starch particles finer than 270 mesh, in the proportion of 3-4% to 10% starch, balance char; adding Water and mixing to form a homogeneous mixture suitable for pressing into the form of briquettes, so pressing said mixture, and then drying the resulting briquettes to a water content of about 4 to 8%.

6. A process according to claim 5 wherein said starch is a cooked starch.

7. A process according to claim 6 wherein said starch is cooked by the heat of the hot char particles.

8. A barbecue briquette consisting essentially of a lignite char and a starch binder therefor, in the proportion of -97% char and 10-3% starch, said char being substantially free of tars and containing l2 to 20% by weight of other volatile combustible matter, and being sized 40 mesh and less, said starch having a particle size less than 200 mesh.

9. A barbecue briquette according to claim 8 wherein said starch is a precooked, substantially protein-free starch.

10. A barbecue briquette consisting essentially of a References Cited in the iile of this patent UNITED STATES PATENTS Cornell Nov. 8, Cann Dec. l5, Schoch Sept. 16, Placek May 3, Swinehart `et al Feb. 4, Leggin Mar. 3, Hall Mar. 20, 

5. A PROCESS FOR TREATING LIGNITE WHICH COMPRISES DRYING CRUSHED LIGNITE AT 125-150*C. TO REMOVE AT LEAST 75% OF ITS WATER CONTENT, SUBJECTING THE DRIED LIGNITE TO HOT PRODUCTS OF COMBUSTION IN A CARBONIZING ZONE AT 500-550*C. TO DRIVE OFF IN THE FORM OF AN OFF-GAS THE REMAINING WATER, THE TARS, AND A PORTION OF THE NON-TAR VOLATILE COMBUSTIBLE MATTER, LEAVING IN SAID CHAR AN AMOUNT OF SAID VOLATILE MATTER EQUAL TO ABOUT 12 TO 20% BY WEIGHT OF SAID CHAR, REMOVING THE TARS FROM SAID OFFGAS AND COOLING IT TO ABOUT AMBIENT TEMPERATURE, CIRCULATING A PORTION OF SAID COOLED OFF-GAS TO COOL THE LIGNITE CHAR EMERGING FROM THE CARBONIZING STEP TO ABOUT 200220*C., CIRCULATING ANOTHER PORTION OF SAID COOLED OFFGAS TO SERVE AS AT LEAST A PART OF THE FUEL SUPPLY FOR FORMING SAID HOT PRODUCTS OF COMBUSTION; CIRCULATING A THIRD PORTION OF SAID COOLED OFF-GAS INTO SAID CARBONIZING ZONE TO CONTROL THE TEMPERATURE THEREOF WITHIN PRESCRIBED LIMITS; THEN SEPARATING OUT ANY RESIDUAL PYRITE FROM THE 